A successful valve replacement or annuloplasty surgery requires accurate measurement of the size of the valve annulus. One of the conventional ways of measuring the valve annulus involves using sizer discs that resemble the shape of the valve annulus, which are provided in various incremental sizes corresponding to the stepped replacement valve sizes. In use, the sizer disc is connected to a rod and is guided into the patient's valve annulus and the surgeon checks the fit of the disc within the valve annulus. If the surgeon is not satisfied with the fit, the surgeon removes the disc from the body and inserts a new disc of a different size into the valve annulus. Once the size of the native annulus is determined, a properly sized replacement valve or annuloplasty device is selected and implanted. This is a time-consuming method and therefore adds to the overall surgery time. Further, the determination of the appropriate size is based on the feeling of the surgeon rather than any mechanical feature, and may not be accurate in some instances.
Alternatively, another conventional way of measuring the valve annulus involves using a heart valve sizer which is introduced into the patient only once. The sizer is capable of gauging a number of appropriate replacement valve or annuloplasty device sizes. These sizers are dimensionally the same as the replacement valves they represent. Due to size constraints, insertion of such heart valve sizers may be a hindrance for certain procedures, especially for minimally invasive surgical incisions such as thoracotomies. With minimally invasive surgical (MIS) type procedures performed through small surgical incisions, the surgeon may not have a good approach angle to the native annulus, thus hindering an accurate tactile feedback to the surgeon when the sizer is in place.
In determining the optimal replacement device for a diseased heart valve, a surgeon generally exerts some level of force to determine a tight fit size. Each surgeon may have a different definition of a tight fit and what is the optimal force that may be exerted. Excessive force can result in inaccurate sizing of the annulus, or even cause tissue damage.
Additionally, a conventional sizer can get entangled in the sub-valvular space of the heart and/or chordae tendineae can become entangled with the external rim of the sizer when the sizer is pushed past the patient's annulus. Disentangling chordae tendineae from the sizer can be time-consuming, delicate and cumbersome. If chordae tendineae are inadvertently withdrawn while the valve sizer is being withdrawn, the mitral structure might collapse.
While the proper sizing determination of a traditional surgical valve may be less sensitive or critical due to the fact that these valves are often parachuted down to the annulus using 12 to 18 sutures which are then used to secure the valve to the annulus, newer valves sometimes employ only three or fewer sutures, which makes sizing accuracy more important. Inaccurate sizing can increase the risks of embolization and paravalvular leaks.
There thus remains a need for an improved heart valve sizer. It is desirable to have a single, one-size-fits-all sizer that could be used to quickly and accurately determine the appropriate valve size for a patient's heart through a minimally sized incision, and which would provide smooth access to the valvular and sub-valvular regions of the heart.